As-built electrical grids supply power based on an expected amount of power that will be used by individual power consumers. However, with the different amount of power consumption depending on season and time and the increase in power consumers, it is not easy to supply an optimal amount of power.
Thus, smart grid systems or micro grid systems have been introduced in which idle power is stored locally in existing electrical grids and is supplied in response to an excess demand for power. Smart grid systems (or micro grid systems) are intelligent electrical grid systems developed by grafting information communication technologies onto power production, transmission and consumption processes to enhance the efficiency of power use through the interaction between power supply and consumption.
In, a power storage system employed in a smart grid or micro grid, one or more large battery systems are installed to control the storage and supply of power. Each of the large battery system includes, for example, one or more battery units selected from cells as the smallest units for power storage and supply, modules as assemblies of a plurality of cells, battery packs as assemblies of a plurality of modules, systems as assemblies of battery packs, and plants as assemblies of a plurality of systems. Due to this construction, the large battery systems can store and supply power of large capacity and high voltage with increasing physical connections between the battery units, such as cells, modules, battery packs and systems.
As described above, generally, the capacity and voltage of power from large battery systems can be controlled by increasing or decreasing the physical connections between the battery units. However, the capacity and voltage of large battery systems are increased to keep pace with the demand for power which increases with the passage of time after initial installation. Accordingly, high stability of large battery systems is needed. However, larger battery systems tend to face greater danger when exposed to natural disasters (e.g., earthquakes, floods and typhoons) and other accidents (e.g., fire and electrical short).
For example, minor problems occurring in some battery units of battery systems may also affect other surrounding battery units, which may lead to major accidents, such as electric shock, fire and explosion.
Therefore, there is a need for a technology that can individually and locally control connection and disconnection between battery units in battery systems as needed to switch between a high capacity and voltage state and a low capacity and voltage state.